This invention relates to the main contact blade assembly for a switching device, and more particularly, to a structural member for transferring a closing force to the contact blade assembly of a circuit breaker.
U.S. Pat. Nos. 4,580,021, 4,524,339 and 4,137,437 illustrate various forms of crossbars (cross arms). In FIGS. 1-5 and 9 of U.S. Pat. No. 4,580,021 a crossbar 36 is illustrated. The crossbar 36 is coupled to a toggle mechanism 60 and intercouples the three poles of the circuit breaker through insulating holders 38. The crossbar is illustrated as having a solid semicircular shaped cross-section. In FIGS. 3a and 5b of U.S. Pat. No. 4,524,339 a square crossbar 46 is illustrated. The crossbar 46 interconnects the blade assemblies 20 and is secured to the top surface of each blade carriers 22. In FIGS. 1, 10 and 13 of U.S. Pat. No. 4,137,437 a cross arm 68 which extends between the individual crossbar and spring holders 64 is illustrated. The cross arm 68 assures that each of the three poles illustrated will move simultaneously upon movement of the operating mechanism 32 to drive the contacts 26, 28 into the closed or open position.
Due to the nature and purpose of a circuit breaker, it is important that the contacts of a circuit breaker are separated as fast as possible when circuit interruption is required. Additionally, it is also important that the contacts of a circuit breaker are closed as uniformly as possible so that the distribution of current flowing through the contacts is substantially uniform. Furthermore, the weight of the crossbar should be such that when the contacts are closed the contacts are not damaged due to the impact force generated at the contacts upon closing. Also, a reduction in the cross bar weight effects a reduced impact energy imparted to the circuit breaker upon opening. Accordingly, it is important that a crossbar be as rigid as possible while also being as light as possible.
Another consideration in providing a crossbar is to ensure that the crossbar is insulated in such a way that arcing is prevented between the poles of a circuit breaker. One way of insulating a crossbar is to coat the crossbar with an insulating material. A problem which arises when coating metallic crossbars with an insulating material is insuring adhesion between the coating and the crossbar.